Effects of mechanical tension on matrix degradation by human periodontal ligament cells cultured in collagen gels

BACKGROUND: Periodontal ligament (PDL) cells are thought to play a crucial role in the remodelling of periodontal tissues during orthodontic tooth movement. OBJECTIVE: The objective of this study was to analyse the effects of mechanical tension on matrix degradation by PDL cells cultured in collagen gels. METHODS: The gels were prepared free-floating or attached to the culture wells and cultured for up to 22 d. In free-floating gels very little mechanical tension is generated within the matrix, whereas in attached gels tension is highly increased. RESULTS: At d 8, free-floating gels had contracted to 2% of their original wet weight. Attached gels had contracted to only 40%, but by d 15 all gels had spontaneously detached from the wells and had contracted rapidly. The collagen content of free-floating gels had decreased to 30% of the initial value at d 22. Collagenase activity was detected in the culture media of the free-floating gels and the presence of matrix metalloproteinases (MMPs) 2 and 9 was shown by zymography. In addition, histological sections showed matrix degradation around the cells. This shows that ligament cells in free-floating gels are actively resorbing the collagen matrix. The collagen content of attached gels did not change during the first 8 d but, after detachment, it rapidly decreased to 2%. Therefore, mechanical tension seems to prevent degradation of the matrix. In contrast, relaxation of the tension enhances the resorptive activity. CONCLUSIONS: The sensitivity of PDL cells to mechanical tension may be essential for the remodelling of periodontal tissues and their adaptation to physiological and orthodontic forces.